The iPad-exclusive app features 400 photographs and hours of video chronicling the development of the World Trade Center, the attacks on 9/11, and the resulting construction of the site’s museum and memorial. Also included is an interactive timeline and links to the National September 11th Memorial Museum site.

Rosenbaum explained why he chose to develop the app for the iPad rather than smaller mobile devices, saying “I wanted it to be more of an immersive experience. The nature of the photographs are so powerful, so to render them in anything but full color seemed wrong to me. And I didn’t want it to be viewed on a phone. I wanted it to be big and glossy.”

‘The 9/11 Memorial’ app is available for free from iTunes until September 12, and will be $9.99 thereafter.